The present invention relates to a new and improved method of continuously casting metals, especially steel, in particular to the continuous casting of billets wherein a multi-phase mixture composed of a liquid inert gas and a particulate additive is introduced into an oscillating continuous casting mold.
It is already known during the casting of steel to apply a flux or slag powder to the molten metal bath, the part of such flux powder in direct contact with the liquid steel melting and exerting a lubricating effect between the cast strand and the walls of the continuous casting mold. During casting of larger strand shapes or formats, there is usually employed in combination with the use of powder a pouring tube which protectively introduces the steel into the mold below the level of the molten bath and separates the flux powder and slag layer from the casting or teeming jet at the region of the bath level. During casting smaller shapes, for instance, billets, it is not readily possible to use pouring tubes, since owing to the given cross-section and the requisite wall thickness of the pouring tube, inadequate space remains between the pouring tube and the cooling mold walls. Therefore, at this location there is formed a bridge of non-molten flux powder and/or solidified steel which can lead to rupture of the casting. If, however, casting is accomplished without using a pouring tube and which flux powder, the drawback exists that the casting or teeming jet undesirably entrains slag particles into the interior of the casting or strand, thereby contaminating the steel. It is for this reason that smaller casting shapes are usually cast while using oil as a lubricant. Yet, when this technique is employed, on the one hand, the bath level no longer is protected from the oxygen contained in the air, and, on the other hand, this technique provides insufficient lubrication during casting, especially when casting free-cutting steel, since the oil is decomposed by the high temperature and the carbon-containing residues afford an inadequate lubrication action. Thus, surface defects appear at the cast strand, which especially during further processing of the strand, such as rolling and possibly drawing, can lead to fissures, and consequently, unusable cast products or only low-quality cast products. Furthermore the effect of the oil can produce so-called pinholes which also impair the quality of the surface of the strand. A further drawback during casting free-cutting steels with oil, especially lead-alloyed free-cutting steels, resides in that during casting there can periodically occur small explosions associated with material being ejected out of the continuous casting mold, thereby endangering the operating personnel.
It is already known to the art during continuous casting of a metal in a mold to use a homogeneous multi-phase mixture. Thus, a substance, for instance, carbon black particles, are introduced into a liquified inert gas, which substance is intended to facilitate the lubrication effect along the walls of the mold. The infed quantity of multi-phase mixture is especially critical when the casting parameters change, such as for instance the casting speed, since with improper calculation of such quantity there occurs either an inadequate lubrication or surface flaws at the cast product.